Idaho's Eastern Snake Plain Aquifer Managed Aquifer Recharge Program

Abstract

The Eastern Snake Plain Aquifer (ESPA), Idaho's largest and most productive aquifer, has experienced substantial decline since the early 1950s due to changing climate conditions, increased demands, and evolving irrigation practices. To address this issue, the Idaho Water Resource Board (IWRB) developed the ESPA Comprehensive Aquifer Management Plan (CAMP). The CAMP outlines methods and goals for the replenishment of the aquifer, including the development of a managed aquifer recharge (MAR) program. In 2014, the State of Idaho has provided dedicated, long‐term funding for the MAR with the goal of achieving an average annual recharge rate of 0.3084 km3 (250,000 ac/ft). Since then, the IWRB has invested over $16 million dollars in investigations and infrastructure improvements to support MAR operations and program build‐out, resulting in an addition of over 62.3 m3/s (2,200 cfs) of instantaneous MAR capacity and total programmatic recharge of over 2.2203 km3 (1.8 million acre‐feet). Overall, the program has added an average of 0.3207 km3 (260,000 ac/ft) per year to the aquifer. Utilizing existing infrastructure and the IWRB's natural flow water rights has significantly reduced programmatic costs. The program's cost for conducting MAR since 2014 is $0.01 per cubic meter or $18 per acre‐foot accounting for capital cost, conveyance fees, operation and maintenance, and monitoring cost. Future capacity increases are planned to further assist the program in capturing excess water when it is available.

Managed aquifer recharge as a strategy to redistribute excess surface flow to baseflow in snowmelt hydrologic regimes

“…Before significant effort is expended characterizing MAR suitability, characterization is required of the flow regime and the status of institutional and legal obligations of SW (downstream uses, water rights, environmental flows) that affect when and how much unallocated streamflow is available for MAR (Figure 4). For example, in the Eastern Snake River Aquifer, Idaho, availability of SW for MAR depends on spring streamflow (Hipke et al, 2022). In dry years, no SW is available for MAR because of the needs of downstream users (e.g., farms, municipalities, hydro-electric power, and environmental flows), while in wet years there is excess available water beyond infrastructure capacity to fully divert and recharge (Hipke et al, 2022).…”

“…For example, in the Eastern Snake River Aquifer, Idaho, availability of SW for MAR depends on spring streamflow (Hipke et al, 2022). In dry years, no SW is available for MAR because of the needs of downstream users (e.g., farms, municipalities, hydro-electric power, and environmental flows), while in wet years there is excess available water beyond infrastructure capacity to fully divert and recharge (Hipke et al, 2022). The efficacy of MAR for baseflow enhancement thus depends critically on the frequency and volume of available unallocated water.…”

The irrigation efficiency trap: rational farm-scale decisions can lead to poor hydrologic outcomes at the basin scale

“…Irrigated agriculture has been in place since 1879 (Van Kirk and Griffin, 1997) and contributes to a $10 billion USD regional economy (Idaho Water Resources Board, 2009). The Henrys Fork overlies the headwater portion of the Eastern Snake Plain Aquifer (ESPA; Figure 1), a 28,000 km 2 unconfined aquifer that provides baseflow to the Snake River system (Hipke et al, 2022). In addition to agriculture, the Henrys Fork hosts a recreational fishery worth $50 million USD (Van Kirk, 2021) and is an important component of local watershed management (Joint Committee, 2018).…”